The range of tasks of infusion therapy is large and essentially lies in the fields of supplying carriers of calories in the case of artificial feeding, of supplying medicines, of regulating the electrolyte balance and the acid-base equilibrium, of supplying liquid for forced excretion of toxins via the kidneys, for example in the event of poisoning by sleeping drugs and the like. Within a hospital, infusions are mainly used in intensive care medicine, in admission and emergency care, in operations, in deliveries, in baby and child care, in functional diagnostics as well as in regular care. An infusion may be performed manually or by using infusion devices.
For selecting the expedient infusion method, the infusion rate that may be used, the infusion duration, the dosing accuracy and the application method that may be used are critical. Most frequent use is made of the conventional, manual infusion method, which is gravity infusion with few requirements placed on the dosing accuracy and the dosing rate. An architecture for such a diffusion is schematically depicted in FIG. 8. The supply of liquid is effected only by the hydrostatic pressure gradient between a patient 1 and an infusion solution filled into a bottle 2.
Assistance is possibly provided by compressing the infusion solution, which may be referred to as a manual pressure infusion. A drip chamber 3 and a roller tubing clamp 4 are provided in the fluid path between the infusion bottle 2 and the patient 1.
In such an arrangement, it is difficult to dose the infusion since the infusion rate, i.e. the velocity of the supply of liquid, can only be regulated manually by closing or opening the roller tubing clamp 4, as is schematically depicted in FIG. 9, which shows three states of a roller tubing clamp; in the left-hand illustration, a fluid tubing 5 is completely pinched off by a roller 6 of the roller tubing clamp, in the central illustration, the fluid tubing 5 is partly pinched off by the roller, and in the right-hand illustration, the fluid tubing 5 is not pinched off by the roller. A corresponding guide 7 is provided which enables the roller 6 to move in the manner shown in FIG. 9 so as to realize different pinch-off states of the fluid tubing 5.
The infusion rate is dependent on a multitude of factors which are hardly or not at all eliminated by a roller tubing clamp. Such factors are, among others, the molding and manufacturing quality of the drip tube within the drip chamber 3 of the infusion set, the drop formation rate, the stability of the delivery pressure, the physical properties of the infusion solution, and the ambient conditions. On account of said factors, only low levels of delivery accuracy of ±20% may be achieved with manual infusion systems, deviations of ±50% being not uncommon.
On account of this low level of delivery accuracy, gravity infusion is applied when infusion therapy allows it. In addition, the physical preconditions for gravity infusion, such as pressure and delivery rate, also need to be met. With gravity infusion, the delivery rate and a catheter closure are measured only manually by counting the drops in the drip chamber. With very low dosing rates, very long observation times may be used in order to recognize a closure. In addition, production of a drip chamber is a cost factor.
By employing infusion devices that use syringe pumps, for example, infusion therapy may be improved in terms of an increase in the infusion rate, an increase in the dosing accuracy, and a guarantee of constant delivery with long-term infusion therapies. On account of said advantages of infusion devices, the spectrum of treatment of infusion therapies may be expanded. In infusions using syringe pumps, the delivery volume is measured only indirectly via the advancement of the syringe motor. The dosing rate is not measured directly, which represents a safety risk. In infusions using syringe pumps, a catheter closure is typically detected by detecting the increase in the motor current. Particularly with small delivery volumes, a closure of the catheter is detected only after long delay times of up to one hour.
A device for supplying fluid to a patient has been known from U.S. 2004/0127844 A1. The device comprises a dispenser, a fluid conduit having an output port suited for coupling to a needle, for example, and a flow state sensor in the flow conduit between the dispenser and the output port. The processor is programmed to cause a fluid to flow to the outlet port. The flow state sensor monitors flow conditions in the fluid path that may occur during operation in order to ensure that the fluid is supplied as intended. The flow state sensor has a diaphragm which partly limits a fluid chamber, so that a pressure within the fluid chamber may be qualitatively evaluated by means of a deflection of the diaphragm. Quantitative measurement of a pressure or determination of a flow rate do not take place.
From U.S. 2007/0151346 A1, an optical pressure monitoring system is known which comprises a conduit from an infusion set as well as an optical signal sensor which is arranged to detect changes in the diameter of the conduit and to thereby determine pressure changes within the conduit. One such sensor may be arranged upstream and downstream from a rotor pump, respectively. A comparable arrangement is also described in U.S. Pat. No. 5,720,721.
U.S. Pat. No. 4,994,035, EP-A1-1769738, EP-A1-1818664 and EP-A2-0401524 each describe sensors for determining pressures in the fluid path of microdosing devices, such as infusion conduits, for example.